Passenger conveyors, such as escalators and moving walks, are well known and efficient devices for transporting people. Escalators are typically used to transport people vertically, such as from one floor of a building to another, and moving walks are more commonly used to transport people horizontally from one point to another in a linear fashion. Some applications for moving walks do require elevation changes and, as a result, have curved sections in the path of travel to provide the needed change in elevation.
As the latter applications become more prevalent, there is a need to provide pallets that can traverse both the linear sections of the path and the curved sections. The need for elevation changes encourages the use of shorter pallets. Shorter pallets accommodate smaller radii in the curved sections. Shorter pallets, however, may become cost prohibitive as the quantity of pallets required for a given length of walk increases.
A typical moving walk is comprised of a truss, a drive sprocket, an idler sprocket, a pair of pallet chains, and a plurality of pallets extending sequentially between and attached to the pallet chains. The drive sprocket engages the pallet chains to drive them through a continuous loop that includes the idler sprocket at the opposite end. The pallet chain includes sequentially coupled chain links and a plurality of rollers that ride in a pair of roller tracks.
Conventional pallets are connected to the pallet chain in one of two methods. The first method is to use a pair of puller wheels disposed on an axle along the forward edge of the pallet. The axle provides support for the forward edge of the pallet and is engaged with the pallet chain to move the pallet with the pallet chain. The wheel may be integral to the pallet chain or may ride in a separate track. The aft edge of the pallet is supported by a second axle having a pair of trailer rollers. The trailer rollers ride in a pair of trailer roller tracks and are not rigidly coupled to the pallet chain. Separate trailer roller tracks are needed to accommodate the curvature of the path of travel as the pallet assembly goes around the sprocket. This method adds complexity and cost to the moving walk as a result of the additional roller track required for the trailer rollers.
The second method uses a sliding block device rather than trailer rollers to accommodate the curvature of the sprocket. In this device, the loads on the aft edge of the pallet are supported by a pin or block that is engaged with a slot on the forward edge of the adjacent pallet. The slot permits the pin or block to move axially while supporting vertical loads on the pallet. Axial movement of the pin or block allows the pallets to move relative to each other as they travel around the sprocket. This method requires a sprocket having significant radial dimension due to the practical limitation on the amount of movement permitted by the sliding block device. This problem is accentuated by shorter pallets that may only extend two chain links. In addition, the sliding engagement between the slot and the block is a source of noise, wear and vibration within the moving walk.
The above art notwithstanding, scientists and engineers under the direction of Applicant's Assignee are working to develop conveyors that minimize cost while providing a durable device that minimizes vibration and noise.